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February/March 2020 Winter's Last Chance Thread


John1122
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1 hour ago, PowellVolz said:

 


Just thinking out loud here but with marginal temps the valley needs a possible inverted trough to stay over the mountains. If it lines up in the valley wouldn’t downsloping become a problem?


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In these cases, the inverted trough is induced by the terrain. The air flow is different on either side of the mountains, so you can basically get a "pinching" (not a very technical way of describing it) between the two flows. Neither side has to deal with much downslope because it creates rising air in the low levels. It is a fixed feature because the mountains are a permanent feature. Hope that makes sense.

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There was a scenario several years back where modeling was not enthused at all about precip into Tennessee.  I remember Robert @ WxSouth ended up picking up on the inverted trough and in the end there was a decent snow from it.  I can't remember the year, but my recollection tells me the basics were familiar... (i.e. overrunning, inverted trough, no defined low, etc.)

Does anyone else remember this event?

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There was a scenario several years back where modeling was not enthused at all about precip into Tennessee.  I remember Robert @ WxSouth ended up picking up on the inverted trough and in the end there was a decent snow from it.  I can't remember the year, but my recollection tells me the basics were familiar... (i.e. overrunning, inverted trough, no defined low, etc.)
Does anyone else remember this event?
I think I remember a handful of those over the years, those are the ones that I remember Morristown having to continually up their forecast snow totals for during the actual events.

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There was a scenario several years back where modeling was not enthused at all about precip into Tennessee.  I remember Robert @ WxSouth ended up picking up on the inverted trough and in the end there was a decent snow from it.  I can't remember the year, but my recollection tells me the basics were familiar... (i.e. overrunning, inverted trough, no defined low, etc.)
Does anyone else remember this event?

It was 2014 I believe. We were in between two systems. About a week before we had a snow/sleet/RZ system that dumped 3-6 inches across the valley before changing to sleet. The inverted trough happened on a Wednesday afternoon and the NWS didn’t start talking about it till the night before. I ended up with 4-5”. A week later we had another overrunning event that was snow to ice to rain. School was out for two weeks.


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In these cases, the inverted trough is induced by the terrain. The air flow is different on either side of the mountains, so you can basically get a "pinching" (not a very technical way of describing it) between the two flows. Neither side has to deal with much downslope because it creates rising air in the low levels. It is a fixed feature because the mountains are a permanent feature. Hope that makes sense.


Absolutely. What I was thinking is if the boundary was in the valley, the SE flow over the mountains might down slop before it was lifted back up. I very well could be overthinking this and cramming to much into a small space.


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This is the MRX discussion from when Robert made the call about enhanced snow over East Tennessee in 2014. I don't quite think it is the same set up as here. 

 

.A STRONG UPPER LEVEL DISTURBANCE WILL MOVE ACROSS THE TENNESSEE

RIVER VALLEY ON WEDNESDAY AFTERNOON AND WEDNESDAY NIGHT...PULLING

MOISTURE WESTWARD FROM A LOW PRESSURE SYSTEM ALONG THE CAROLINA

COAST. THIS SYSTEM WILL BRING THE POSSIBILITY OF SIGNIFICANT

SNOWFALL ACCUMULATIONS OVER MUCH OF EAST TENNESSEE...SOUTHWEST

VIRGINIA...AND EXTREME SOUTHWEST NORTH CAROLINA BY EARLY THURSDAY

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This is the MRX discussion from when Robert made the call about enhanced snow over East Tennessee in 2014. I don't quite think it is the same set up as here. 
 

.A STRONG UPPER LEVEL DISTURBANCE WILL MOVE ACROSS THE TENNESSEE

RIVER VALLEY ON WEDNESDAY AFTERNOON AND WEDNESDAY NIGHT...PULLING

MOISTURE WESTWARD FROM A LOW PRESSURE SYSTEM ALONG THE CAROLINA

COAST. THIS SYSTEM WILL BRING THE POSSIBILITY OF SIGNIFICANT

SNOWFALL ACCUMULATIONS OVER MUCH OF EAST TENNESSEE...SOUTHWEST

VIRGINIA...AND EXTREME SOUTHWEST NORTH CAROLINA BY EARLY THURSDAY


I’m just about 100% positive that’s the inverted trough snow we got. I remembered it was on a Wednesday and was pretty sure it was in 14’


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15 minutes ago, PowellVolz said:

 


Absolutely. What I was thinking is if the boundary was in the valley, the SE flow over the mountains might down slop before it was lifted back up. I very well could be overthinking this and cramming to much into a small space.


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When it comes to downslope winds in East TN, I would never say never. There are so many possible ways for it to happens. I assume that areas along the mountains of SE TN would have a slightly better chance of that happening, due to the surface winds being SE on the other side of the mountains in that area. I think areas farther to the northeast would be pretty safe from downslope in this situation.

 

 


Just to be clear since there is some discussion about this now, this isn't a significant inverted trough. It is very subtle (mainly seen in wind field), but it maybe just enough to help us out a little. Especially in eastern counties. And the northerly flow down the valley could help areas further south with temps, as Jeff mentioned.

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5 minutes ago, John1122 said:

This is the MRX discussion from when Robert made the call about enhanced snow over East Tennessee in 2014. I don't quite think it is the same set up as here. 

 

 

 

Yep, totally different from the first few words..... lol

nice find........You always amaze me with your records and recollections.  You are a great asset to our group!!

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8 minutes ago, Vol4Life said:

Remind me...what model are those plumes based off of?

SREF..kind of like the ensemble of the NAM. Ran in between the NAM runs, usually a good indicator of where the next upcoming NAM run may go.

 

 Currently, the Weather Research and Forecasting Non-hydrostatic Mesoscale Model (WRF-NMM) model is run as the NAM, thus, three names (NAM, WRF, or NMM) typically refer to the same model output. The WRF replaced the Eta model on June 13, 2006.[1] The model is run four times a day (00, 06, 12, 18 UTC) out to 84 hours. It is currently run with 12 km horizontal resolution and with three-hour temporal resolution, providing finer detail than other operational forecast models. The NAM ensemble is known as the Short Range Ensemble Forecast (SREF) and runs out 87 hours.

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